The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A gas-fired, warm air furnace that operates at two fixed gas flow rates is generally referred to as a two-stage furnace. Two stage furnaces are frequently selected by homeowners over single stage furnaces because they offer increased performance and comfort. However, in two stage heating furnaces, the furnace control is only configured for operating a two stage gas valve at a fixed high gas flow rate and a fixed low gas flow rate. Such two stage gas valves are not capable of providing variable heating, and cannot be readily replaced by modulating gas valves. Accordingly, a need still exists for an improved valve unit and associated control for present two stage heating systems.